GrainGenes
A Database for Triticeae and Avena
Nikitenko et al., pp. 51-56
II. 22. Some characteristics for formation of quantity and quality of the crop within hybrid populations of different generations of spring barley.
G.F. Nikitenko, Research Agricultural Institute of Central Regions in the Non-Chernozem Zone, Moscow-Nemchinovka, 143013, U.S.S.R.; M.A. Polukhin and V.A. Gorshkova, Research Agricultural Institute of Central Chernozem Regions named after V.V.Dokuchayev, 397463, Talovsky District, Voronezh Region, U.S.S.R.
Development of a variety which is capable of producing high yields of grain of good quality under different conditions, has always been a most important objective in breeding of cereals. According to this fact the yield of grain is considered to be the general criterion in breeding programs. It is considered to be character which is to be stabilized, because yield is the integrated sum of effects, acting in each case of environment factors, in which potential possibilities of definite genotypes are manifested.
Superiority of heterozygotes as compared with homozygotes considering resistance to environment conditions and reproduction of normal phenotype provides heterozygotes with quite certain advantage which is used by hybrid population. Therefore the up-to-date breeding programs involve in all cases artificial crossing, because there is a widely spread opinion that hybridization always produces a positive effect in characteristics and traits important for national economy.
But as a matter of fact it is far from being like that. Breeding practice proves that while crossing of highly valuable parents, the hybrids do not possess these characters. And at the same time hybrids of high value often result from crossing of parents which do not have these valuable characters.
One of the most important problems, therefore, in modern breeding is the development of methods of precise identification of desirable genes, resulting in high yields in parents and generations, i.e., in hybrid population.
As the result of long-term breeding activity with spring barley, we have accumulated extensive experimental material on peculiarities of the formation process in hybrid populations of different generations. The most important results of this work are set forth below.
Since 1965, 20 hybrid combinations of spring barley have been developed and studied. Their multiplication and testing was done by the Ohio method, which allowed us to plant in the field all generations simultaneously by 1978: F1- F12 (Fig. 1). The sowing of 1978: F1 - in accordance with availability of seeds, and F2 - F12 on plots of the 7m2 size with the nutrition area for each plant - 15 x 3 cm. Productivity and its elements have been studied as well as protein content in grain of three hybrid combinations.
Figure 1. Scheme of producing hybrid populations of different generations.
The analysis of productivity of hybrid populations in different generations (Table 1) shows that its level is different and it is increasing in later generations. Thus, in combinations Europeum 353/133 x Nutans 187 the average yield in F1 - F3 was 493.1 + 37.1 in the plot, and variation coefficient (V%) - 13.0%, in F4 - F6 correspondingly 892 + 70.3 g, V - 13.6% and in F7 - F12 - 973.3 + 43.8 g. and V - 11%. The same regularity was observed in other crossing combinations as well - Spartan 11 x Nutans 187, Gerta x Nutans 187, but absolute values of productivity and its elements were different.
The diagram of the yielding capacity in F1 - F12 of Spartan 11 x Nutans 187 hybrid combination shows the same regularity - increase of the productivity level from early to later generations of hybrid population. Thus, in F1 - F3 the yield (according to average data) was equal to 579.6 + 37.7 g, and V - 11.3%, and in the diagram its level is lower. In F4 - F6 the yield increases up to 752.3 + 47.7 g (V = 10.9%), and in F7 - F12 - up to 973.3 + 41.8 g (V = 11.3%) to which the highest upper plateau corresponds in the diagram (Fig. 2).
The results of the analysis of hybrid population yield in different generations by elements of its structure permit to conclude that their role in formation of the crop is different and depends mainly on traits of parental forms, involved in combination of crossing. For instance, in hybrid population Europeum 353/133 x Nutans 187 the yield increases in generations due to productive branching and the mass of 1000 seeds, and in Gerta hybrid x Nutans 187 - due to the mass of 1000 seeds.
Hybridological analysis of F1 - F12 plants proved that with the age hybrid population involves specimen close to parental forms. Thus, if in F2 of the combination Spartan 11 x Nutans 187 the plants with characters of both parents were observed (with dense head but with smooth awns and on the contrary - with loose head and notched awns), starting with F7 - F8 there were the forms which prevailed in population, repitting the type of initial parents (Table 2.).
The change of protein content is of inverse character to the yield: increased protein content corresponds to lower production of hybrid population and on the contrary.
Summing up the above, it's possible to say that the increase of the yield in hybrid population of spring barley, starting from early and to the direction of later generations, is explained by main preconditions of the hypothesis of genetic homeostasis and all consequences (Lerner, 1954). According to this hypothesis, under the effect of natural selection genotypes are developed in the population. They provide with rather steady reproduction of "optimum phenotype". As far as such an important trait as yield, this homestasis means its stability under permanently changing conditions of environment, which reflects the practical importance of this phenomenon for plant breeding. In this case the structure of population is modified in such a way that the balanced frequencies of alleles are established, and they provide the hybrid population with the definite level of heterozygosis, when adaptability of specimen, composing the population, reaches the maximum in later generations.
The obtained experimental data are in contradiction with the assertion of some authors, according to which the decrease of non-additive variance is noted in comparison with the additive one with the age of hybrid population, and in connection with this fact, expedience of selection of initial plants in early generations is noted, for instance in F3 (Grafius et al., 1952), and on the contrary, such selection is more effective in later generations of the hybrid population, when its yield is getting more steady and higher (Wiebe et al., 1968).
References:
Grafius, J.E., W. L. Nelson, and V.A. Dirks. 1952. The heritability of yield in barley as measured by early generation bulked progenies. Agron. J. 48:7.
Lerner, C. M. 1954. Genetic homostasis. Edinburgh.
Wiebe, G. A. et al. 1968. Barley: Origin, botany, culture, winterhardiness, genetics, utilization, pests. U.S. Department of Agriculture, Washington, D.C.